Not Applicable.
Not Applicable.
(1) Field of the Invention
This invention relates to an organic foundry binder containing an alkyl resorcinol, or preferably a readily available mixture of alkyl resorcinols, and derivatives thereof. Preferably, the organic foundry binder is a furan binder. Foundry mixes are prepared by mixing the binder with a foundry aggregate. Foundry shapes (molds and cores) are prepared by shaping the mix and allowing it to cure to form a workable foundry shape. The invention also relates to the preparation of metal castings using the foundry shapes and the metal castings prepared with the foundry shapes.
(2) Description of the Related Art
In the foundry industry, one of the processes used for making metal parts is sand casting. In sand casting, disposable foundry shapes (usually characterized as molds and cores) are made by shaping and curing a foundry mix, which is a mixture of sand and an organic or inorganic binder. The binder is used to strengthen the molds and cores and can be heat cured, catalytically cured, or cured with a combination of heat and a catalyst.
One of the processes used in sand casting for making molds and cores is the cold-box process. In this process, a gaseous curing agent is passed through a compacted shaped mix to produce a cured mold and/or core. Some commonly used binders in this process are phenolic urethane binders, acrylic binders, epoxy-acrylic binders, furan binders, and alkaline phenolic resole binders.
One of the most commercially successful cold-box binders is the phenolic-urethane binder system, which is cured with a gaseous tertiary amine catalyst. See for example U.S. Pat. Nos. 3,409,579, 3,429,848, 3,432,457, and 3,676,392. The phenolic-urethane binder system consists of a phenolic resin component and polyisocyanate component, which are mixed with sand prior to compacting and curing to form a foundry mix. Such phenolic-urethane binders used in the cold-box process, have proven satisfactory for casting such metals as iron or steel which are normally cast at temperatures exceeding about 1400xc2x0 C. They are also useful in the casting of light-weight metals, such as aluminum, which have melting points of less than 800xc2x0 C.
There are disadvantages to using phenolic-urethane binders in the cold-box process. Both the phenolic resin component and polyisocyanate component generally contain a substantial amount of organic solvent which can be obnoxious to smell. Additionally, these binders contain small amounts of free formaldehyde and free phenol, which may be undesirable. Because of this, there is an interest in developing binders, which do not use organic solvents and do not contain free formaldehyde or free phenol.
Additionally, when the two components of the phenolic-urethane binder system are mixed with the sand to form a foundry mix, they may prematurely react before curing with the gaseous catalyst. If this reaction occurs, it will reduce the flowability of the foundry mix when it is used for making molds and cores, and the resulting molds and cores will have reduced strengths.
Another commonly used process in sand casting for making molds and cores is the no-bake process. The phenolic urethane binder system is one of the most commercially successful binders used in this process. However, in the no-bake process, a liquid curing catalyst (an amine in the case of phenolic urethane binders) is used and mixed with binder and foundry aggregate before shaping.
Because the molds and cores made by the no-bake process are usually quite large, weighing from 0.2 pounds to several tons, it is important to formulate a foundry mix which will provide sufficient worktime to allow time to shape the foundry mix in the pattern. Worktime is defined as the time interval after mixing the binder components and sand in a pattern, and the time when the foundry shape reaches a level of 60 on the Green Hardness xe2x80x9cBxe2x80x9d Scale Gauge sold by Harry W. Dietert Co., Detroit, Mich. On the other hand, the striptime for removing the foundry shape from the pattern must be diminished so that high productivity can be obtained. Striptime is the time interval after mixing the binder components and sand in a pattern, and the time when the foundry shape reaches a level of 90 on the Green Hardness xe2x80x9cBxe2x80x9d Scale Gauge. For commercial purposes, a desired worktime ranges from 2 minutes to 1.5 hours and a desired strip time of 4 minutes to 3 hours. The foundry shapes produced must have sufficiently high tensile strengths, so they can be handled after the striptime has elapsed. The cores and molds must also produce useful castings, i.e. castings that do not have defects such as veining, porosity, lustrous carbon, penetration, and erosion defects.
The foundry industry continues to be interested in no-bake binders that do not contain free formaldehyde and phenol; which have useful worktimes and striptimes for high production operations; and that produce foundry shapes with sufficiently high tensile strengths that can be used to make casting with minimal defects. Consequently, there is an interest in developing foundry binders with lower levels of VOC emissions, free phenol, and free formaldehyde that do not have unpleasant odors and generate little smoke during the core making and castings process.
Acid cured no-bake furan binders are attractive alternatives to the phenolic urethane no-bake binder system because they preferably do not contain free phenol, free formaldehyde, high levels of VOC emission, result in unpleasant odors, and generate lower smoke during the core-making and casting processes. However, one of the major problems with these binders system, is that they do not cure as rapidly as the phenolic urethane no-bake binders and the immediate tensile strengths of cores made with the binder systems create handling problems. Because of this, the furan binders are modified to increase their reactivity by incorporating other polymer or reactive monomers into the furan binder, e.g. urea formaldehyde resins, phenol formaldehyde resins, resole resins, resorcinol, bisphenol A tar, etc. Nevertheless, these modifications do not provide the cure speed and/or immediate tensile strengths that are needed in high productivity core shops.
In addition to increasing the cure rate of the binder, it is desirable to identify additives that impart greater mechanical strength to the cores and molds. These additives are also desirable for improved humidity and temperature resistance in the core and mold making process. Additionally, additives which lower free formaldehyde (scavenge), by reaction with it, are desirable.
Finally, it is desirable to identify materials that are lower cost than current product constituents are, but which are capable of performing in a manner that is comparable, or superior to the present constituent.
U.S. Pat. No. 5,847,058 discloses storage-stable phenol-aldehyde resole resins modified with an alkyl resorcinol modifier, preferably a readily available mixture of alkyl resorcinols. The modified resins are useful in the production of a wood composite (such as plywood, oriented strandboard, or fiberboard).
All citations referred to under this description of the xe2x80x9cRelated Artxe2x80x9d and in the xe2x80x9cDetailed Description of the Inventionxe2x80x9d are expressly incorporated by reference.
This invention relates to a foundry binder system comprising:
A. an organic foundry binder; and
B. an Alkyl resorcinol ad mixtures thereof.
Foundry mixes are prepared by mixing the binder with a foundry aggregate. Foundry shapes (molds and cores) are prepared and allowed to cure to form a handleable or workable foundry shape. In the no-bake process, the catalyst is mixed with the aggregate and binder before shaping, while in the cold-box process the foundry mix is shaped and then exposed to a gaseous curing catalyst. The invention also relates to the preparation of metal castings using the foundry shapes and the metal castings prepared with the foundry shapes, particularly by the no-bake process. It is surprising that the improved properties result when the binders are used in the no-bake process, because no similar improvements result when the binders are used in the phenolic-urethane cold-box process.
The use of the alkyl resorcinol in the binder provides faster curing speeds for the binder and/or results in cores with improved immediate, intermediate, and/or long term tensile strengths. The addition of the alkyl resorcinol to the furan no-bake binder results in particular advantages. The advantages of the furan/alkyl resorcinol binder over the conventional no-bake furan binder system are as follows:
(1) The furan is highly soluble and compatible with the alkyl resorcinol, resulting in low viscosity binders where the components are highly compatible.
(2) Furfuryl alcohol typically used in furan binders can be reduced without adversely affecting the cure speed of the binder and the tensile properties of the cores prepared with the binder.
(4) Cores prepared with the furan binder containing an alkyl resorcinol cure rapidly and uniformly throughout, even when less furfuryl alcohol is used in the binder. The cure speeds of these binders match the cure speed of commercially successful phenolic urethane no-bake binders. Thus, they can be handled without breaking sooner, typically in 8 to 10 minutes, preferably less than 8 minutes. These benefits also make these binders suitable for high-speed core production foundries.
(5) The binders are advantageous from an environmental standpoint because they eliminate the need for phenolic or urea-formaldehyde additives. The result is that the binders do not contain free phenol or free formaldehyde, require little or no volatile organic solvents, and produce little odor and smoke during core-making and casting.
Not Applicable.